How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 8 August 2017

Implications of spreadability for dairy and bakery products

The spreadability of margarine and butter is of paramount importance for consumer acceptability.
It is a physical property and results from the fact that these products
consist of a dispersion of solid fat crystals in liquid oil.

The
ratio of solid to liquid fat in a product is probably the most
important factor determining hardness and spreadability. However,
hardness and softness are not the only factors influencing
spreadability; smoothness and brittleness are also important.

This has
more to do with the size and shape of fat crystals than with their
amount. A product is smooth when the crystals are relatively small and
this is possible with hard as well as soft butter or margarine.
Brittleness is associated with high solid fat content and/or excessive
size of fat crystals. Under these conditions large crystals interlock to
result in a brittle product, though such conditions rarely occur in
soft butter or margarine.

Butter is always hard to spread when it
comes straight from the fridge. Margarine producers manufacture soft
margarines by using a mixture of vegetable oils instead of dairy fat.
The graph below illustrates this point in the comparison of three fat
types using the Spreadability Rig.

Test and results
During
the test the force is seen to increase until the point of maximum
penetration depth of the cone probe. This peak force value (or force at
another chosen penetration depth) can be taken as the "Firmness" at the
specified depth. A firmer sample also shows a correspondingly larger
area which represents the total amount of force (otherwise referred to
as 'work of shear') required to perform the shearing process. Both of
these values have been shown to rank samples in the same order of
spreadability (and firmness), but for some samples one many prove to be
more suitable than the other. The probe then proceeds to withdraw from
the sample and any adhesive characteristics are indicated by a negative
force region on the curve.

The rheological properties of a
semisolid food, such as margarine are important in process design,
quality control, and development of new products. Soft or tub margarine
is mainly used as a spread for toast and sandwiches. When taken from the
refrigerator, a margarine should spread evenly and smoothly with no
syneresis and separation. The graph (right) shows the difference in spreadability
properties of a table spread tested at 5°C and 20°C.

Low-fat spreads

Since
the early 1990s we have seen the advent of very low fat spreads (25%
fat and below) in the European market. Being under strong public
pressure to produce healthier fat mimetics, manufacturers have attempted
to develop new spreads with the emulsion phase inverted (the fat phase
is dispersed within the aqueous matrix) whilst attempting to achieve the
required 'plasticity'. Unsophisticated mixing of ingredients is likely
to result in brittle or elastic preparations, making them unsuitable for
spreading.

Cake products

Fats and oils perform
many functions in cake products - they trap in air during the creaming
process, lubricate the gluten and starch particles (breaking the
continuity of the gluten/starch structure of the cell walls for a tender
crumb), and emulsify and affect water holding capabilities for moisture
retention and shelf-life properties.

Margarines or fats that are
too hard impair the beating activity and result in poor mixing.
Conversely, margarines can be too soft to provide sufficient resistance
to the mixing blades to produce a lump free, well-emulsified mix or
batter. Butter and other milk-fat derivatives are widely used in bakery
products, especially in cakes, because of their desirable flavour.
Although bakers continue to favour the use of butter, variations in
butter quality and functionality have encouraged a search for fat
alternatives to be used in cake recipes.

Margarines and baking
fats can be suitable for producing cake products if the melting range,
consistency and whipping properties are good.

Puff pastry

In
general, a margarine for puff pastry applications must be plastic, dry,
tough and have a constant consistency. During lamination the margarine
or fat must spread easily without forming lumps.

The
characteristic features of a puff pastry shortening are plasticity and
firmness. Plasticity is necessary to form smooth, unbroken layers of fat
between dough layers during repeated folding and rolling operations to
achieve over 1200 layers. Firmness is equally important, because soft
and oily fat products can be absorbed by the dough, destroying its role
as a barrier between the dough layers. A five-to six-fold increase in
the height of a test pastry shell after baking can be achieved provided
that the fat contributes a satisfactory performance.

Conclusion

Testing
the wide choice of fat alternatives for their suitability as a
replacement for traditional fats is now possible both precisely and
objectively. The range of ingredients has broadened to provide
manufacturers with new opportunities for gaining a marketing, textural
or economic selling edge. Parallel with this, artisan skills must give
way to objective measurement of ingredient performance parameters in
order to create products which are of reproducible quality and
consistency over large batches.

Fats and oils are fundamentally
important ingredients affecting a wide range of properties. Texture
analysis systems provide computer-controlled precision with a wide range
of probes, fixtures and temperature control equipment which enable
manufacturers to select ingredients for performance, quality and
economy.

We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once
your measurement is performed, our expertise in its graphical
interpretation is unparalleled. Not only can we develop the most
suitable and accurate
method for the testing of your sample, but we can also prepare analysis
procedures that obtain the desired parameters from your curve and drop
them into a spreadsheet or report designed around your requirements.